I asked OT member hairy hen about the PCM track, who is the go to guy about audio stuff around here and this is what he said for a more comprehensive answer:

When the 1993 laserdiscs were produced, the audio tracks were taken from original source material in 4-track format: left, right, center, and mono surround. These channels were downmixed to matrixed stereo and are intended to be expanded back into surround sound (pseudo-5.1) through the use of an upmixing algorithm in a receiver. Depending what kind of receiver you have, there may be several options available to choose from, but if you have Dolby Prologic II, that is what I would recommend using. This will separate the 2.0 mix into multiple channels, with the left, right, and center information going to their respective speakers, and the mono surround will be heard equally from both rear speakers. If you have a subwoofer, the low frequency information will be separated out and will play from there. These mixes do have a fair amount of bass in them–it was added in specifically because the 70mm theatrical mixes had substantial bass content–although on the 1993 versions isn’t as loud as a more modern 5.1 mix might be due to the lack of a separate LFE channel.